The present invention relates to plasma containment devices and to plasma confinement systems such as those employed in thermonuclear fusion studies. It is applicable to both toroidal confinement systems, such as tokamaks, levitrons or stellarators and linear confinement systems as employed in linear theta pinch and linear machines. The invention relates in particular to beam limiter devices comprising ringshaped or helical structural members. The individual rings and individual turns of a helical beam limiter may be of circular, elliptical, D-shaped and other closed or nearly closed configurations.
Although some plasma systems employ strong magnetic fields, for plasma confinement, solid rings as beam limiters may be positioned at intervals along the internal surface of the vacuum vessel or liner containint the plasma. The beam limiter ring can thereby shade a portion of the internal surface from plasma particle impact and the resulting erosion.
The beam limiter rings employed heretofore have suffered from a number of shortcomings. Plasma particles colliding with the beam limiter have severely disintegrated portions of the ring facing the plasma. The collision of plasma particles on the limiter causes vaporization, sputtering and blistering with accompanying release of beam limiter materials. This released material on entering the plasma produces serious power losses due to bremsstrahlung and line radiation that can lead to an abrupt end to the plasma discharge. Some of these problems have been discussed and illustrated in "Plasma Wall Interactions in the T.F.R. Machine" by Rebut et al., Journal of Nuclear Materials, Vol. 53, page 16, Aug. 1974.
Previously employed beam limiters have comprised rings having rectangular and convex-curved cross sections taken on a plane cutting the ring at two diametrically opposed locations. Both of these cross-sectional configurations have permitted sputtered, blistered or vaporized limiter materials to readily enter the plasma region. Rings having convex cross sections with apexes towards the plasma suffer from the additional disadvantage of decreased material in the portion of the ring nearest the plasma.